1. Field of the Invention
The present invention relates to an integrated circuit, and more particularly to an analog to digital conversion circuit configured to convert an analog value into a digital value.
2. Description of the Related Art
A digital integrated circuit receives a digital signal and performs an operation to output a digital signal, some integrated circuits, however, may receive an analog signal. For processing an analog signal, an integrated circuit generally includes an analog to digital conversion circuit (ADC) configured to convert an analog signal into a digital signal. For example, a signal inputted to a sensor included in a device for processing an image is an analog signal. The signal should be converted into a digital signal for internal information processing. Because information received by the sensor of an image processing device is typically a minuscule signal, the image processing device should include an ADC with high resolution to recognize the minuscule signal.
A high performance ADC with a high resolution and a sampling speed of tens of millions Hz has been required in not only image processing systems such as a digital camera, a digital camcorder and a digital TV, but also communication systems such as a wireless communication device, an asynchronous digital subscriber loop (ADSL) device and an IMT-2000 device.
For an ADC, several-types of structures have been suggested. For example, there is a flash structure, a folding structure, a sub-ranging structure, a pipeline structure, and the like. Recently, among those structures, the pipeline structure has been widely used because it can satisfy high-speed signal processing conditions and high resolution conditions, and also optimize operation speed, power consumption and scalability. The ADC with a pipeline structure includes plural stage pipelines. Herein, each stage can be a single-bit structure deciding a 1-bit data or a multi-bit structure deciding two or more bits data.
A plurality of unit circuits included in an ADC having a pipeline structure each converts a partial portion of an analog signal into a predetermined-bit digital signal and delivers a remaining portion of the analog signal to the next unit circuit. The ADC requires an amplifying circuit configured to amplify the remaining portion of an analog signal before the remaining portion is delivered. However, the amplifying circuit consumes a lot of power, so this is a handicap of the ADC with a high resolution.